• The First Law of Thermodynamics states that energy can neither be created nor destroyed, only altered in form.

• In analyzing an open system using the First Law of Thermodynamics, the energy into the system is equal to the energy leaving the system.

• If the fluid passes through various processes and then eventually returns to the same state it began with, the system is said to have undergone a cyclic process. The first law is used to analyze a cyclic process.

• The energy entering any component is equal to the energy leaving that component at steady state.

• The amount of energy transferred across a heat exchanger is dependent upon the temperature of the fluid entering the heat exchanger from both sides and the flow rates of thse fluids.

• A T-s diagram can be used to represent thermodynamic processes.

The First Law of Thermodynamics is referred to as the Conservation of Energy principle, meaning that energy can neither be created nor destroyed, but rather transformed into various forms as the fluid within the control volume is being studied.

The energy balance spoken of here is maintained within the system being studied. The system is a region in space (control volume) through which the fluid passes.

The various energies associated with the fluid are then observed as they cross the boundaries of the system and the balance is made.

A system may be one of three types: isolated, closed, or open. The open system, the most general of the three, indicates that mass, heat, and external work are allowed to cross the control boundary.

The balance is expressed in words as: all energies into the system are equal to all energies leaving the system plus the change in storage of energies within the system.